The detection of syphilis by the determination of Wassermann antibodies in physiological fluids, particularly in serum is carried out on a large scale. Such determination is particularly important for the control of blood and serum utilized for transfusions.
It is known that cardiolipin, a natural phospholipid extracted from ox heart muscle, can be utilized as a hapten for the serological detection of Wassermann antibodies. Cardiolipin has the general formula ##STR2## wherein ##STR3## represents an unsaturated fatty acid residue. Attempts to replace cardiolipin with analogue which might have a simpler structure and, therefore, could be synthesized have not been satisfactory. Until now, such analogues as have been synthesized have demonstrated little or no activity in the serological syphilis test in comparison with cardiolipin as is reported, for example, in Nature, Vol. 206, p. 935 (1965). Suitable analogues of cardiolipin are provided in accordance with the present invention.